Devolitilizing process using rabbles and forming devices for conveying materials

ABSTRACT

In a rotary hearth furnace utilizing rabbles to move the coke in windrows across the hearth of the furnace, a row-leveller can follow at least one of the rabbles to level off the peaks of the windrows, thus reducing maximum bed thickness and increasing heat transfer into the bed of material.

United States Patent Schilson [451 Mar. 28, 1972 [54] DEVOLITILIZING PROCESS USING RABBLES AND FORMING DEVICES FOR CONVEYING MATERIALS [72] Inventor: Robert E. Schilson, Littleton, C010.

[73] Assignee: Marathon Oil Company, Findlay, Ohio [22] Filed: Dec. 29, 1969 [21] Appl. No.: 888,698

521 US. Cl ..201/33, 201/27, 201/40, 202/100, 202/103, 202/117, 202/136 [51] Int. Cl ..Cl0b 7/02, C1013 47/20 [58] Field ofSearch ..202/117,104, 218,102,103; 201/32, 33, 40, 27, 36, 37; 263/26 [56] References Cited UNITED STATES PATENTS 3,448,012 6/1969 Allred ..202/103 3,470,068 9/1969 Kemmerer et a]. ..202/1 17 X 3,475,286 10/1969 Kemmerer et al. 2,997,426 8/1961 2,676,006 4/1954 985,053 2/1911 Noad ..202/l 17 Primary Examiner-Norman Yudkofi Assistant Examiner-David Edwards Attorney-Joseph C. Herring, Richard C. Willson, Jr. and Jack L. Hummel [57] ABSTRACT In a rotary hearth furnace utilizing rabbles to move the coke in windrows across the hearth of the furnace, a row-leveller can follow at least one of the rabbles to level off the peaks of the windrows, thus reducing maximum bed thickness and increasing heat transfer into the bed of material.

6 Claims, 5 Drawing Figures PATENTEDmzamz 3,652,404 swan 1 [IF 3 M/VENTOR ROBERT E. SCHILSON ATTORNEY PATENTEDMAR28 1972 3,652,404

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' l/VVEIV ROBERT E. SCHILS BY ATTORNEY DEVOLITILIZING PROCESS USING RABBLES AND FORMING DEVICES FOR CONVEYING MATERIALS CROSS REFERENCES TO RELATED APPLICATIONS U.S. Patent applications Ser. No. 755,595 and 613,145 now U.S. Pat. No. 3,448,012) are in the same field.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to distillation, processes, thermolitic of the general sort classified in class 201 of the United States Patent Office and relates generally to subclass 18 (utilizing apparatus of particular compositions), and in preferred embodiments, to sub-class 27 thereof (including burning of vaporized product).

2. Description of the Prior Art 1. U.S. Pat. No. 3,227,627 relates to methods for heat treatment of material which yields oxidizable volatile matter under heat; U.S. Pat. No. 3,448,012 relates to a concentric partition utilized in a rotating furnace in which material is moved across the surface of the hearth by means of rabbles; British Pat. No. 1,055,857 (of which U. S. Pat. application Ser. No. 432,197 filed Jan. 4, 1965 is a counterpart) teaches apparatus for moving material across a hearth which has the configuration of a series of steps by first contacting the materials with a rabble which extends partly through the bed to push the upper portion of the bed onto the next lower step and then contacting the bed with a second rabble which extends more deeply then pushes the remainder of the bed onto the next lower step. None of the prior devices have taught the present invention which, in its preferred embodiments, can minimize bed thickness by forming a substantially level bed (or a bed of continuously tapering thickness) upon the hearth.

b. Other U.S. patents have taught devices for transporting material on rotating disks or hearths; for example, U.S. Pat. No. 1,885,673; 2,1 12,401; 2,89l,32l;and 1,989,662.

GENERAL STATEMENT OF THE INVENTION The present invention is to be limited only by the claims appended hereto and the abstracts, examples, and summaries included within the present disclosure are to be taken as being merely illustrative of the invention. However, the invention offers apparatus and means for providing a maximum of heat transfer into a bed within a furnace which is heated by heat radiating from the interior of a chamber located above the hearth of said furnace. This maximizing of heat transfer is highly useful to provide both high throughput of treated product per hour of operation and also to provide high uniformity of treated product. By maintaining a smooth and level (or more nearly smooth and level) bed of material lying on the hearth and by raising material to the surface from the interior of the bed, the present invention reduces the possibility of underheated material or overheated material passing through the furnace.

The devices and processes of the present invention are useful with a wide variety of feed materials, e.g., non-carbonaceous materials such as lime, dolomite, cement rock, calcium oxide, various carbonate sulfates and chlorides, and also,

particularly preferred, can be used with carbonaceous materials including so-called non-caking coals, anthracite coal, wood products, green petroleum coke, pellets or briquets containing controlled percentages of bituminous coking coal, fluid petroleum coke, and delayed petroleum coke. The invention is particularly preferred for the calcining of so-called raw or green" delayed petroleum coke to remove volatile matter. Materials which yield oxidizable volatile matter on heating are particularly preferred because these permit the volatile matters to be oxidized in the chamber above the hearth to provide all or a portion of the heat required for the devolatization and other treatment of the material disposed on the hearth.

In accordance with the invention, the material to be heated is first placed upon the hearth at a delivery point. The hearth is continuously moving relative to the rabbles and forming devices discussed later. Either the hearth may be moving, the rabbles and forming devices may be moving, or both may be moving at speeds which are sufficiently different to cause substantial relative motion between the hearth on the one hand and the rabbles and forming devices on the other.

The material deposited on the hearth is contacted by a first rabble which forms it into a windrow, having a substantially triangular-cross-section. The base angles of the windrows will normally correspond to the angle of repose of the material being treated.

A forming device then makes contact only with an upper portion of the triangular-cross-section of the windrow. This forming device will deflect material from the upper portion so as to truncate the cross section of the windrow and reduce its average depth.

The truncated window so formed will then rest substantially undisturbed upon the hearth until substantial movement of the hearth relative to the rabbles has occurred. Preferably, the windrow will lie undisturbed for approximately one full revolution of the hearth. Thereafter, the windrow is contacted by a second rabble which causes all or most of the material in the windrow to be transported a short distance across the hearth to form a new windrow which is somewhat closer to the discharge point at which the residuum of treated material is eventually removed from the hearth. The new windrow will usually be separated from the old windrow by a furrow, that is, a V-shaped declevity. The new windrow is then contacted by a second forming device similar to the first, which deflects material from the upper portion of the new windrow, truncating it and deflecting material into the adjacent furrows. By adjusting the forming device, sufficient material may be removed from the windrow so as to just fill in the furrows, leaving a level bed of material disposed on the hearth. This level bed provides a minimum thickness of material on the hearth.

Heat radiating downward contacts the bed and heats the outermost particles to a maximum temperature. It has been found that a temperature gradient exists between the outermost surface of the bed and the particles near the hearth. By minimizing the thickness of the bed, this temperature gradient can be minimized so that more nearly uniform temperature is experienced by all particles at every given moment. This provides product uniformity and permits higher throughput through a furnace of a given hearth area. This is true because throughput is generally limited by the minimum heat treatment which will be experienced by a relatively few particles. In a smooth bed, the difference between the heat treatment experienced by an average particle and the minimum heat treatment experienced by any particle is reduced and the throughput can therefore be increased. As the rabble contacts the windrow, the natural action in shifting the material across the hearth to form the new windrow causes material which was previously deeper within the body of the windrow to appear at or near the surface of the new windrow. This turningover of the bed assists in obtaining a uniform product.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a section view of a preferred rotary hearth furnace according to the invention.

FIG. 2 is a cross-sectional detail showing the rabbles and forming devices of the present invention.

FIG. 3 is a plan view showing schematically the positioning of the rabbles and forming devices in the furnace of FIG. 1.

FIG. 4a is a cross-sectional view of a windrow after it has been formed by a rabble.

FIG. 4b is a cross-sectional view of a windrow after it has been truncated by the action of a forming device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a furnace having a rotary hearth 10 with an inner hearth surface 11 sloping from the outer periphery downwardly to a central axially extending soaking pit 12 integral with and depending from the hearth 10. The rotary hearth is supported on spaced rollers 13 mounted on a furnace frame 14. The hearth is rotated by a motor and a rack and pinion drive in a conventional manner for rotary hearth furnaces. A curb 15 extends vertically above the hearths surface 11 at its outer periphery and carries a waterseal l6 filled with water 17. Sand, fluid coke, or similar pulverized material can be used instead of water, if preferred.

The furnace frame 14 carries roof beams which support a cast refractory roof 21 having a central flue 22. The roof 21 has a depending wall 23 carrying flange 24 which extends into the water 17 carried in waterseal 16. The roof 2] is provided with wickets or nozzles 25 which receive air from duct 26 mounted on the furnace frame 14. The ports 25 direct gases gently downward toward the hearth. Side walls 23 of the roof are provided with ports 27 receiving air from duct 28. The ports 27 direct air across the hearth in a radial direction.

Burners (not shown) are provided in the roof of the inner chamber to bring the furnace to operating temperature and to provide additional heat for those reactions which are not completely autogenetic. A feed chute 30 passes through the roof 21 adjacent the side wall 23 and is provided with a vertically adjustable delivery end 31 extending to point adjustably selected to deliver a selected thickness of feed onto hearth surface 11. A radially extending U-shaped rabble pit 32 (shown in FIG. 2) is formed in the roof and extends radially from the flue 22 to the roof wall 23. The bottom of this pit 32 is provided with slots adapted to slidably receive rabbles 34 and forming devices 35. Rabbles 34 and forming devices 35 may be solid or of hollow platelike structure with inner vertical baffles depending upon the temperature involved. For the higher temperatures, of course, the latter is preferred. Each baffle is provided with inlet and outlet coolant conduits which also act as supports for the rabbles and forming devices. Coolant such as water or air is delivered to the inlet and into forming device 35 on one side of the baffle and then under the baffle to the opposite side of the forming device and out through the outlet pipe 37 (not shown). Refractory seals 38 are provided on conduits 36 and 37 to fit into slot 33. The conduits 36 and 37 are held between two angular forming device holders which are held together by bolts. The forming device holders 39 and 40 are fastened between adjustable carrier angle beams and by bolts. Vertical adjustment screws are provided at each end of each adjustable carrier beam. These screws bear on fixed forming device beams which extend across the rabble and forming device pit 32 and serve to vary the clearance between the lower end of the rabbles 34 and the upper surface ofthe hearth 11.

A rotary discharge table is provided beneath the soaking pit 12 to receive the output of the furnace. A fixed discharge spout or plow 51 is mounted in frame 14 between the soaking pit l2 and discharge table 50. Spout 51 is provided with a peripheral trough 52 carrying sand 53 into which a depending flange 54 on the soaking pit extends to form a seal.

The operation of the furnace described above is as follows. The burners are fired to bring the furnace up to the desired temperature which depends upon the nature of the material being devolatilized or calcined. Material to be treated is fed through feed chute 30 and is continuously spread to the desired thickness and width along the outer periphery of hearth surface 11. As the hearth rotates, the material encounters the rabbles 34. Each rabble deflects material striking it into the next adjacent concentric windrow ring so that the flow of material from the the periphery of the hearth surface 11 to the soaking pit 12 is generally in spiral concentric ringlike windrows, each of greater width so that as the diameter of the ringlike windrows becomes smaller, the area becomes greater providing a uniform maximum depth. After encountering each rabble, the material in the windrow formed by the rabble moves a short distance and then encounters forming devices 35. Each forming device deflects material from the top of the triangular-cross-section windrow formed by the rabble and thus truncates the triangular-cross-section. The material from the upper portion of the windrow is deflected into the previous (or next) adjacent furrow. By adjusting the clearance between the bottom of the forming devices 35 and the upper surface of the hearth 11, a sufficient quantity of material may be deflected from the upper portion of each windrow to just fill the adjacent furrow, thus creating a substantially level bed of material on the hearth,

The concentric spiral ringlike windrows are diagrammatically illustrated in FIG. 3, together with the relative position of each rabble and each forming device with respect to the windrows. The rabbles tend to cause mixing and inversion of the bed several times as the material moves downwardly from the hearth periphery to the soaking pit. This permits more uniform heating and provides a more uniform product.

Exhaust gases exit through flue 22.

The temperature during devolatilization of the coke in this particular preferred embodiment is maintained at approximately 2400 F by adjusting the inflow of air so as to oxidize all of the volatile combustible matter which is driven off from the material lying on the hearth. The invention is, of course, capable of operating over a wide range of temperatures which will be selected according to the raw material being fed and the treatment to which it is to be subjected.

Among the possible modifications which can be made to the invention where desired by the particular circumstances are the use of specialized forming devices so cut on the lower edge as to provide a slightly rippled or slightly roughened surface to the material lying on the hearth; noncircular hearths, e.g., the tunnellike configuration illustrated in FIG. 1 of the aforementioned U.S. Pat. No. 3,227,627, rotating hearths in which the feed is at the center and the discharge is at the outer periphery, specialized coolants other than water for cooling the forming devices or the rabbles or both such as liquid metals, e.g., potassium-sodium mixtures, as well as furnaces in which the hearth is still and the rabbles move over the hearth.

Also, in certain instances it may be useful to have the forming devices following only the last few rabbles prior to the discharge point, or alternate rabbles or some other set of selected rabbles. The forming devices may be set so as to cause the bed to be thinner at some points, e.g., near the discharge point where the material will generally need to experience its highest temperature. Multiple rabbles or forming devices can be arranged along the windrow to successively partially move or form a single windrow in stages.

What is claimed is:

1. In a continuous process for removing volatile matter from material which yields such volatile matter under heat, which process comprises continuously delivering such material at a delivery point onto a continuously moving substantially imperforate hearth having substantially no discontinuities, continuously removing residuum from the continuously relatively moving hearth at a discharge point and subjecting said material to heat radiating downward from the interior surface of a chamber at least a portion of which is above said hearth, and transporting material toward said discharge point by the action of at least one rabble depending downward into said material, said rabble being disposed to form said material into a windrow extending the direction of the relative motion of said hearth, said windrow having substantially triangular cross section and having an adjacent furrow, the improvement comprising, in combination:

a. contacting said triangular-cross-section of said windrow with a forming device depending downwardly into only an upper portion of said triangular-cross-section of said windrow, said forming device being disposed to deflect material from the upper portion of said windrow into said furrow so as to truncate at least a portion of said triangular-cross-section whereby the average depth of said windrow is decreased.

2. The process of claim 1 wherein the volatile matter is oxidizable and wherein at least a portion of said heat is obtained by burning at least a portion of said removed volatile matter within said chamber.

tacted by a forming device shortly after said windrow is formed by a rabble.

6. The process of claim 1 wherein the quantity of material deflected from the upper portion of said windrow is substantially sufficient to fill said furrow to a height equal to the height of said windrow after it has been truncated whereby a level bed is formed on at least a portion of said hearth. 

2. The process of claim 1 wherein the volatile matter is oxidizable and wherein at least a portion of said heat is obtained by burning at least a portion of said removed volatile matter within said chamber.
 3. The process of claim 1 wherein the hearth is a circular hearth which rotates with relation to said rabble and said forming devices.
 4. The process of claim 1 wherein a plurality of rabbles are spaced to form at least three windrows successively moving said material from said delivery point toward said discharge point.
 5. The process of claim 4 wherein each windrow is contacted by a forming device shortly after said windrow is formed by a rabble.
 6. The process of claim 1 wherein the quantity of material deflected from the upper portion of said windrow is substantially sufficient to fill said furrow to a height equal to the height of said windrow after it has been truncated whereby a level bed is formed on at least a portion of said hearth. 